With the caveat that these are consumer-grade drives being used in a very high-vibration environment under stressful conditions, Backblaze's Brian Beach noted that they've excluded the Western Digital Green 3 TB and Seagate LP (low power) 2 TB drives. These drives tend to spin down when not in use and then spin right back up, which causes a lot of wear and tear and a high failure rate in the Backblaze environment. It's not that they're bad drives -- they're just not suited for the high-stress environment of a storage farm.

As you can see in the graphic at the top of this post (taken from the Backblaze study), Hitachi drives tend to have the lowest annual failure rates for Backblaze, followed by Western Digital drives. Seagate drives have a much higher failure rate, although the larger 3 and 4 TB drives tend to be more reliable than the 1.5 TB model. Of the 1.5 TB Seagate drives, the Barracuda LP is the most reliable, but the Barracuda Green drives are -- to quote Beach -- "dropping like flies."

Beach notes that "if the price were right, we would be buying nothing but Hitachi drives. They have been rock solid, and have had a remarkably low failure rate." I've always been a fan of Western Digital drives, so I was happy to see that they also tend to be survivors in the Backblaze world. You can see the relative survival rates for Hitachi, Western Digital and Seagate drives in the graphic at the bottom of this post.